1. Field of the Invention
The present invention relates to a method, an apparatus, and a computer program for generating three-dimensional shape data or volume data.
2. Related Art of the Invention
A method named “shape from silhouette” has been known as a prior art method for generating three-dimensional shape data for an object.
In the shape-from-silhouette method, a plurality of images of an object are obtained by photographing (or imaging) from diverse points of view, whereby the three-dimensional shape of the object is reproduced. That is, in the shape-from-silhouette method, on the basis of each image of the object photographed in a direction of sight, the region of presence of the object which reflects the shape viewed in the direction of sight is described as a set of voxels in the three-dimensional image space. Then, a set composed of voxels each belonging to all of the above-mentioned sets of voxels describing the images viewed in the diverse directions of sight is obtained as the object in the three-dimensional image space.
Nevertheless, in the prior art shape-from-silhouette method, the shape of the object is represented only by the presence or absence of each voxel. That is, the attribute of each voxel is two-valued such as to indicate whether the voxel is included inside the object or not.
Accordingly, the resolution of the voxels directly provides the resolution on the object surface. Thus, in order to obtain a more precise three-dimensional representation of the object, voxels of higher resolution are necessary. This needs a huge number of voxels, and hence causes the problem of a significant increase in the memory capacity necessary for storing the volume data.
In addition to this problem, in the shape-from-silhouette method, depressed or concave portions of the object are not expressed in the silhouette images. Accordingly, there is the problem that such recesses can not be reproduced.
Another prior art method for reproducing the three-dimensional shape of an object uses a range sensor (three-dimensional measuring instrument) for measuring the object by a non-contact method such as light-section method. Nevertheless, in such a method using the range sensor, there is the problem that data is not obtained for the object surface having very low surface reflectivity, whereby the three-dimensional shape of such surface portions is not reproduced.